Vanadyl oxalate compounds and process for producing same

ABSTRACT

Vanadyl oxalate compounds, particularly vanadyl oxalate monohydrate and vanadyl oxalate sesquihydrate, are prepared by reacting vanadium pentoxide with oxalic acid dihydrate or anhydrous oxalic acid in an acetic acid solvent system.

United States Patent [151 3,689,515

Smith, Jr. Sept. 5, 1972 [54] VANADYL OXALATE COMPOUNDS 1,914,557 6/1933Craver ..260/429 R AND PROCESS FOR PRODUCING 3,018,255 1/1962 Banks..252/455 R SAME [72] Inventor: William Novis Smith, Jr., Exton, OTHERPUBLICATIONS Pa, l 93 4 l H Zolotavin et a1. Th. Neorg. Khim (J. Inorg.Chem. Assrgnee: llioote Mineral Company, Exton, U.S.S.R.) Vol. 1, No.4,1956. p. 101- 107 s a. r [22] Filed: June 4, 1971 PrimaryExaminer-Delbert E. Gantz Assistant ExaminerA. P. Demers [2]] Appl'lsooss Attorney-l-lowson and Howson [52] Cl ..260/429 R, 252/431 C,260/429 J [57] ABS I'RACT [51] Int. Cl. ..C07f 9/00 Vanadyl oxalatecompounds, particularly vanadyl oxa- [58] Field of Search ..260/429 R,429 J late monohydrate and vanadyl Oxalate sesquihydrate are prepared byreacting vanadium pentoxide wi'th ox- [56] References Cited alic aciddihydrate or anhydrous oxalic acid in an UNITED STATES PATENTS aceticacid solvent system.

12/ 1910 Rehlander ..260/ 429 R 8 Claims, 3 Drawing Figures PATENTEDsEP5 m2 FIGI.

B WAVELENGTH (MICRONS) FIGZ.

0 1 0 I 9 HM ww w R m K w 3 9 1 W6 I N F E E V m 7 0 0 5 v WAVELENGTH(MICRONS) AT TVS.

VANADYL OXALATE COMPOUNDS AND PROCESS FOR PRODUCING SAME BACKGROUND OFTHE INVENTION Vanadium containing compounds are widely used as oxidationcatalysts. Typical catalysts are prepared by depositing vanadiumcontaining compounds on a suitable support and activating the vanadiumcompounds by well known procedures. Aqueous solutions of vanadyl loxalate are frequently utilized to prepare vanadium containingcatalysts, a typical catalyst prepared from vanadyl oxalate beingdescribed in US. Pat. No. 3,01 8,255. Vanadyl oxalate is particularlydesirable for use in preparing such vanadium containing catalysts since,when activated by decomposition with heat, the vanadyl oxalate isconverted to vanadium pentoxide or vanadium dioxide, the latter beingformed if the thermal decomposition is carried out in the absence ofoxygen, with carbon dioxide and water being liberated. The catalystformed is thus free of extraneous anions or cations.

Heretofore, vanadyl oxalate compounds have been prepared by a fusionreaction between vanadium pentoxide and oxalic acid or by reacting thesecompounds in water at elevated temperatures. These procedures aredescribed in articles by Sathyanorayana et al. in the Journal ofInorganic and Nuclear Chemistry, Volume 27, p. 297 (1965) and Satapathyet al. in the Indian Journal of Chemistry, Volume 1, p. 757 1963). Thefusion reaction produces a fused mass of vanadyl oxalate dihydrate whichmust be ground before it can be conveniently utilized. When vanadiumpentoxide and oxalic acid are reacted in water, an aqueous solution ofvanadyl oxalate is initially produced. Recovery of the solid vanadyloxalate dihydrate from the aqueous solution, which is usuallyaccomplished by solvent evaporation, is time consuming since the vanadyloxalate dihydrate crystallizes from the solution at a very slow rate.Thus, neither of these processes produces vanadyl oxalate compounds in asolid, particulate form which can be immediately utilized in, forexample, catalyst manufacturing processes. Other methods for producingvanadyl oxalate compounds are disclosed in US. Pat. Nos. 979,887,1,914,557, and 3,025,132. In these processes vanadyl oxalate is normallyisolated and recovered in hydrated forms such as vanadyl oxalatedihydrate, trihydrate, or tetrahydrate.

It is apparent that the multihydrated vanadyl oxalate compounds areundesirable since shipping or transporting of these materials from theirproducer to a catalyst manufacturer involves the expenses of shippingthe large amounts of water of hydration associated with the vanadyloxalate. Therefore, a need exists for a process for producing vanadyloxalate compounds with low water of hydration moieties associatedtherewith.

Accordingly, it is an object of this invention to provide a process forpreparing vanadyl oxalate compounds with little water of hydrationassociated therewith.

It is a further object of this invention to produce vanadyl oxalatemonohydrate and vanadyl oxalate sesquihydrate.

A still further object of this invention is to provide a convenient andeconomical process for producing solid vanadyl oxalate compoundsdirectly in particulate form without the need of evaporation ofsolvents.

DESCRIPTION OF THE INVENTION According to this invention, theabove-described objects and advantages are obtained in a process forpreparing vanadyl oxalate compounds which comprises reacting about onemol of vanadium pentoxide with from about 3 to about 3.5 mols of anorganic acid selected from the group consisting of oxalic acid dihydrateand anhydrous oxalic acid in a solvent con- 0 sisting essentially ofacetic acid containing not more V205 ar-1,0,0, 2H2O 2voc o -2H o+7H,o+

V205 i 3H2C204 2VOC204' 1 (III) The vanadium pentoxide reactant employedin the above equations can be any commercially available form of V 0preferably in finely-divided form, that is, having a particle size ofabout l00 mesh (Tyler Series).

The other principal reactant in the illustrated reactions is oxalicacid. In the reaction with vanadium pentoxide to produce vanadyloxalate, the oxalic acid serves not only as a reducing agent, but alsoas a source of the oxalate anion. Oxalic acid is normally available asthe dihydrate and it is in this form that the present process generallyutilizes this reactant. It has been found, however, that anhydrousoxalic acid is preferred when the process is utilized to produce vanadyloxalate sesquihydrate.

The reaction between vanadium pentoxide and oxalic acidstoichiometrically requires 3 mols of oxalic acid for each mol ofvanadium pentoxide. The reaction preferably will be carried out with thestoichiometric proportions of reactants; however, the reaction willproceed with a combination of reactants within the range of from about 3to about 3.5 mols of oxalic acid per mol of vanadium pentoxide. Excessoxalic acid reduces the reaction time required to produce vanadyloxalate monohydrate.

The present process is carried out in a solvent consisting essentiallyof acetic acid containing not more than 30 percent, by weight, water.Hydrated forms of vanadyl oxalate have been found to be almostcompletely insoluble in glacial acetic acid. Thus, acetic acid is anideal solvent for the reaction between vanadium pentoxide and oxalicacid, since the hydrated forms of vanadyl oxalate can be easilyrecovered in a dry powder. The preferred form of acetic acid utilized iscommercially available glacial acetic acid which con- 3 tains about 0.5percent water. More dilute acetic acid solutions, such as thosecontaining up to as much as 30 percent, by weight, of water may,however, be utilized as the solvents in this process. It has also beenfound that the presence of water in the acetic acid solvent increasesthe rate of reaction between vanadium pentoxide and oxalic acid.However, since the vanadyl oxalate compounds are water soluble, solventsystems containing large amounts of water, e.g. greater than 30 percent,by weight, are avoided to eliminate the possibility of loss of productto the solvent. It has been found that acetic anhydride, and acids suchas formic acid and propionic acid are not useful solvents for thisprocess.

In carrying out the process, the vanadium pentoxide and oxalic acid aremixed in the acetic acid solvent and the mixture is heated. The reactionmay be carried out at any temperature between 50 C. and reflux, however,the reaction rate becomes significant at about 70-75 C.- The preferredtemperature range for the reaction is from about 100 to about 120 C.Lower reaction temperatures favor the formation of vanadyl oxalatedihydrate, but the reaction rate is quite slow below 70 C.

The reaction mixture is heated for from about 2 to about hours, theduration of the reaction determining in large measure the particularhydrated form of vanadyl oxalate recovered as the product of thereaction. For example, if the reaction between stoichiometricproportions of vanadium pentoxide and oxalic acid dihydrate is carriedout in glacial acetic acid at reflux for from one to two hours, theproduct will be vanadyl oxalate dihydrate which has a characteristicpeacock blue color. Heating the same reactants under the same conditionsfor about three hours produces a greenishblue mixture by analysis foundto be about 78 percent vanadyl oxalate dihydrate and 22 percent vanadyloxalate monohydrate. If reacted for about four hours, this reactionproduces a mixture found to be about 1 l percent vanadyl oxalatedihydrate and 89 percentvanadyl oxalate monohydrate, and if the reactionis carried out for at least about 5 hours, the product analyzes 99.5percent vanadyl oxalate monohydrate, a bright blue compound. It is thusapparent that the length of reaction time is one factor determining theparticular hydrated form of vanadyl oxalate recovered in this process,another factor being the amount of water in the reaction system. Thus,for example, if the solvent system initially contains about 5 percent,by weight, water, the vanadyl oxalate monohydrate can be formed in about3 A hours.

Vanadyl oxalate sesquihydrate is prepared by reacting vanadium pentoxidewith anhydrous oxalic acid at reflux for at least about 5 hours. As seenin equation III, the total amount of water in this reaction is low incomparison to that found in the reactions producing the dihydrated andmonohydrated forms of vanadyl oxalates. The sesquihydrated form ofvanadyl oxalate, which has a pale blue-gray color, may also be obtainedby conversion of vanadyl oxalate dihydrate by drying at 100 C. under 0.1mm Hg for 15 hours.

Following the reaction, the reaction mixture is cooled and the vanadyloxalate compound which is formed is isolated from the reaction mixtureby filtration and the residue is dried to remove any traces of aceticacid, advantageously under a vacuum of from about 0.1 to about 1 mm ofmercury, at a temperature of from about to about C. The hydrated formsof vanadyl oxalate produced by this method contain less water ofhydration and proportionally more vanadyl oxalate than those produced byprevious methods. Accordingly, use of vanadyl oxalate monohydrate orvanadyl oxalate sesquihydrate in preparing vanadium containing catalystsis especially advantageous due to the increased vanadium content ofthese compounds.

The novel compound vanadyl oxalate monohydrate is recovered as a bluecrystalline powder which exhibits a strong infra-red absorption peak ina hydrocarbon mull at 985 cm as depicted in FIG. 1. Vanadyl oxalatesesquihydrate is recovered as a pale blue-gray crystalline powder whichexhibits a strong infra-red absorption peak in a hydrocarbon mull at 980cm with a small shoulder at 1010 cm as depicted in FIG. 2. In contrast,as shown in FIG. 3, vanadyl oxalate dihydrate exhibits a strongabsorption peak in a hydrocarbon mull at 1,010 cm". The vanadyl oxalatecompounds are soluble in water and alcohol and are deliquesent tovarious degrees. These hydrated forms of vanadyl oxalate may be used toproduce the vanadium containing catalysts discussed above. In addition,they may be utilized to produce selective oxidation catalysts useful incommercial processes such as the conversion of 2-butene to maleicanhydride.

The following examples are set forth as illustrative of this invention:

EXAMPLE 1 A round-bottom, (three-necked, 500 ml. flask is equipped witha stirrer, thermometer, and reflux condenser. The flask is charged with30 g. vanadium pentoxide, 63.9 g. of oxalic acid dihydrate and 252 ml.of

glacial acetic acid. The reaction mixture is heatedto a temperaturemaintained between 108 and 118 C. for 2 hours, cooled to roomtemperature, filtered, and the filtrate is discarded. The solid is driedat 80 C. under a vacuum of 0.25 mm of Hg for 5 hours. The peacock blueproduct, vanadyl oxalate dihydrate [VOC I-I '2I-I O], weighs 61.1 g. fora yieldof 99.6 percent. The vanadium analysis is 26.7 percent and theoxalate is 46.3 percent, balance water. Vanadyl oxalate dihydrateexhibits an infra-red absorption peak in a hydrocarbon mull of 1,010 cmas shown in FIG. 1.

EXAMPLE 2 Utilizing the apparatus and the reactants of Example 1, themixture is heated to a temperature maintained between 108 and 118 C. for3 hours, cooled to room temperature, filtered, and the filtrate isdiscarded. The solid is dried at 80 C., under a vacuum of 0.25 mm of Hgfor 3.5 hours. The product weighs 60.3 g for a yield of 98 percent. Theproduct is a greenishblue mixture of 78 percent, by weight, vanadyloxalate dihydrate and 22 percent, by weight, vanadyl oxalatemonohydrate. The vanadium analysis is 27.4 percent and the oxalate is47.9 percent, balance water.

EXAMPLE 3 Utilizing the apparatus and the reactants of Example 1, themixture is heated to a temperature maintained between 108 and 118 C. forfour hours, cooled to room temperature, filtered, and the filtrate isdiscarded. The solid is dried at 80 C. under a vacuum of 0.25 mm of Hgfor 5 hours. The product weighs 56.0 g for a yield of 97 percent. Theproduct is a mixture of 11 percent, by weight, vanadyl oxalate dihydrateand 89 percent, by weight, vanadyl oxalate monohydrate. The vanadiumanalysis is 29.1 percent, and the oxalate is 49.6 percent, balancedwater.

EXAMPLE 4 i Utilizing the apparatus and reactants of Example 1, themixture is heated to a temperature maintained between 108 and 118 C. for5 hours, cooled to room temperature, filtered, and the filtrate isdiscarded. The solid is dried at 90 C. under a vacuum of 0.15 mm of Hgfor 5 hours. The product weighs 57.2 g for a yield of 99.5 percent. Thevanadium analysis is 29.2 percent and the oxalate is 50.8 percent,balance water. The bright blue product is vanadyl oxalate monohydrate[VOC O H which exhibits an infra-red absorption peak in a hydrocarbonmull of 985 cmas shown in FIG. 2.

EXAMPLE 5 Utilizing the apparatus of Example 1, the flask is chargedwith 30 g. vanadium pentoxide, 75 g. oxalic acid dihydrate, 200 ml.glacial acetic acid, and ml. of water. The reaction mixture is heated toa temperature maintained between 108 and 118 C. for 3.5 hours, cooled toroom temperature, filtered, and the filtrate is discarded. The solid isdried at 80 C. under a vacuum of 1.0 mm Hg for 5 hours. The product,vanadyl oxalate monohydrate, weighs 55.2 g for a yield of 96.5 percent.The analysis for vanadium is 29.3 percent, and for oxalate is 50.4percent, balance water. Vanadyl oxalate monohydrate exhibits aninfra-red absorption peak in a hydrocarbon mull of 985 cm as showninFIG. 2.

EXAMPLE 6 Utilizing the apparatus of Example 1, the flask is chargedwith 10 g. vanadium pentoxide, 50.2 g. anhydrous oxalic acid, and 70 ml.of glacial acetic acid. The reaction mixture is heated to a temperaturemaintained between 1 10 and 118 C. for 5 hours, cooled to roomtemperature, filtered, and the filtrate is discarded. The solid is driedat C. under 0.03 mm Hg for 5 hours. The pale blue-gray product, vanadyloxalate sesquihydrate [VOC O 1.5H O], weighs 19.6 g. for a yield of 98percent. The vanadium analysis was 27.5 percent and the oxalate is 46.7percent, balance water. Vanadyl oxalate sesquihydrate exhibits aninfrared absorption peak in a hydrocarbon mull of 980 cm with a smallshoulder at 1,010 cmas shown in FIG. 3.

What is claimed is:

1. A process for preparing vanadyl oxalate compounds which comprisesreacting about one mol of vanadium pentoxide with from about 3 to about3.5 mols of an organic acid selected from the group consisting ofanhydrous oxalic acid and oxalic acid dihydrate in a solvent consistingessentially of acetic acid containing not more than 30 percent, byweight,

water over a period of from a out 2' to about 5 hours.

2. A process accordmg to c arm 1 wherein said reaction is carried out ata temperature ranging from about 50 C. to about reflux.

3. A process according to claim 1 wherein about one mol of vanadiumpentoxide is reacted with about three mols of oxalic acid dihydrate inglacial acetic acid at a temperature ranging from about 100 to about 120C. for about 1 to about 2 hours to produce vanadyl oxalate dihydrate.

4. A process according to claim 1 wherein about one mol of vanadiumpentoxide is reacted with about three mols of oxalic acid dihydrate inglacial acetic acid at a temperature ranging from about to about C. forat least about 5 hours to produce vanadyl oxalate monohydrate.

5. A process according to claim 1 wherein about one mol of vanadiumpentoxide is reacted with about 3.5

mols of oxalic acid dihydrate in about 95 percent acetic acid at atemperature ranging from about 1 10 to about 120 C. for about 3.5 hoursto produce vanadyl oxalate monohydrate.

6. A process according to claim 1 wherein about one mol of vanadiumpentoxide is reacted with about three mols of anhydrous oxalic acid inglacial acetic acid at a temperature ranging from about 100 to about 120C. for at least about 5 hours to produce vanadyl oxalate sesquihydrate.

7. Vanadyl oxalate monohydrate.

8. Vanadyl oxalate sesquihydrate.

2. A process according to claim 1 wherein said reaction is carried outat a temperature ranging from about 50* C. to about reflux.
 3. A processaccording to claim 1 wherein about one mol of vanadium pentoxide isreacted with about three mols of oxalic acid dihydrate in glacial aceticacid at a temperature ranging from about 100* to about 120* C. for about1 to about 2 hours to produce vanadyl oxalate dihydrate.
 4. A processaccording to claim 1 wherein about one mol of vanadium pentoxide isreacted with about three mols of oxalic acid dihydrate in glacial aceticacid at a temperature ranging from about 110* to about 120* C. for atleast about 5 hours to produce vanadyl oxalate monohydrate.
 5. A processaccording to claim 1 wherein about one mol of vanadium pentoxide isreacted with about 3.5 mols of oxalic acid dihydrate in about 95 percentacetic acid at a temperature ranging from about 110* to about 120* C.for about 3.5 hours to produce vanadyl oxalate monohydrate.
 6. A processaccording to claim 1 wherein about one mol of vanadium pentoxide isreacted with about three mols of anhydrous oxalic acid in glacial aceticacid at a temperature ranging from about 100* to about 120* C. for atleast about 5 hours to produce vanadyl oxalate sesquihydrate.
 7. Vanadyloxalate monohydrate.
 8. Vanadyl oxalate sesquihydrate.